When the 33 Chilean miners emerged from underground before a worldwide audience of over a billion, they made a pact not to speak about what had happened underground. Now six of them remember the untold story of the first 17 days - when no-one outside knew if they were alive. Filming down a Chilean mine, the programme explores the nightmare of living in the dark tunnels half a mile underground, eating a spoonful of tuna every two days and not knowing if you would ever be found.